U.S. Pat. No. 6,270,295 describes a tool with a selectively biased member and method of using the tool. In one or more embodiments disclosed therein, the radial position of a blade carried on the end of a rotating tool, such as a reamer or a boring bar, is controlled by fluid pressure. In particular, fluid pressure is applied to an internal bore or cavity to effect radial movement of the blade in order to control the diameter of the hole being bored.
One of the methods disclosed in U.S. Pat. No. 6,270,295 of using one of the embodiments of the tool involves controlling the blade position based on the axial position of the blade. This method produces an axis symmetrical bore. FIGS. 9, 10 and 11 of U.S. Pat. No. 6,270,295 illustrate a method which compensates for material deformation in a workpiece. The specific method described in relation to these figures addresses axial deformation in a bore, in which the workpiece bows inward near the top of the hole due to material properties inherently in the workpiece.
An error can also present itself in which the radius/diameter of the bore is not constant based on angular position. FIG. 1 is a diagrammatic top view of a non-axis symmetric bore 2 in which the radius/diameter is not constant, varying based on angular position. In FIG. 1, non-axis symmetric arc 4, shown as a localized void of material extending outwardly from 36° to 144°, deviating from the perfectly circular bore represented by arc 2a. Non-axis symmetric arc 4 may alternatively protrude into the bore 2. As seen in FIG. 2, which is a fragmentary, diagrammatic side view of bore 2 taken along line 2-2 of FIG. 1, non-axis symmetric arc 4 may be located at any position along axis 6 of bore 2, and does not have to be longitudinally constant.
There are three basic sources of the error. 1) the non-axis symmetric arc 4 may result from manufacturing error in which a perfectly circular bore is not formed; 2) the bore may become deformed as a result of assembly, such as by way of example, distortion in a cylinder bore when the bolts holding the cylinder head are tightened, even if within specification; and 3) thermal distortion.
FIGS. 3A and 3B diagrammatically illustrate top and side views, respectively, of a cylinder bore 8 showing distortion occurring due to assembly. There is illustrated concave portion 10 extending outwardly and convex portion 12 extending inwardly, both of which are spaced down from surface 14 and occupy different angular positions, although at the same axial location.
Such error can be directly addressed by use of the tools and methods disclosed in U.S. Pat. No. 6,270,295, within the scope of the claims thereof. FIGS. 4A-E illustrate an embodiment of the tool, similar to the embodiments described in U.S. Pat. No. 6,270,295.